1. Field of the Invention
The present invention relates to a touch signal probe and particularly to an improved touch signal probe suitable for use in electrically detecting a contact with an object to be measured.
2. Description of the Prior Art
There is well known a three-dimensional measuring machine for measuring the size and shape of an object placed on a measurement base or a system for measuring the position of an object relative to the tool post of a machine tool. In these measuring systems, a touch signal probe is normally mounted on a table movable relative to the object in any direction. Such a touch signal probe is adapted to produce an electric signal at the output thereof when it contacts the object, the output signal being used to accurately operate the measuring system.
In other words, when the object is contacted by the contactor of the touch signal probe, this contactor is inclined so that the contacts will be separated resulting in the electrical detection of the contact with the object.
In such a kind of system, normally, the contacts used to detect the inclination of said contactor comprises a movable contact and a fixed contact which are brought into engagement with each other when the contactor is in its non-contact with the object. On the other hand, if the contactor contacts the object, the contactor is inclined to open the contacts. This is electrically detected to know the contact of the object with the contactor.
The movable contact is normally urged toward the fixed contact under the action of a spring such that the contacts will not accidentally be separated from each other for any reason such as vibration or others.
If the urging force of the spring is not properly set, however, the contact of the contactor with the object may not properly be detected. If the urging force of the spring is too strong, the sensitivity of detection will vary in different directions in which the contactor contacts the object. On the contrary, if the urging force of the spring is too small, the contactor will tend to swing. This raises such a problem that the contactor cannot return to its accurate home position at all times if the contactor is of the inclination type. As a result, the accuracy of measurement will be degraded.